Week 1: Introduction to CS21 and Python Programming

Week 1 Goals

Understand course format and policies
Learn about the CS network and Linux
Learn to use the Visual Studio Code editor (code)
Learn how to write and run python programs
Learn basic python syntax and semantics
Learn the string, integer, and float data types

Course Overview

Login with CS account. Reset your Password if needed.
Open your browser and bookmark the course webpage https://www.cs.swarthmore.edu/courses/CS21/S24/
Review the course syllabus
Read Lab 0 before lab.
Attend Lab
This course has a final exam. Do not schedule end of semester travel plans until we know the final exam time (scheduled by the Registrar)

Get Week 1 In-class Code

To copy over the week 1 in-class example program, do the following (If you have trouble with either of these steps, ask a Ninja or your professor for help):

Create a w01-intro in your cs21/inclass subdirectory, and cd into it:

$ cd ~/cs21/inclass
$ mkdir w01-intro
$ cd w01-intro
$ pwd
/home/yourusername/cs21/inclass/w01-intro

Copy over the week 1 files into your w01-intro subdirectory (check that they copied successfully copied by running ls:
```
$ cp ~admin21/public/w01-intro/* ./
$ ls
greeting.py  numbers.py  welcome.py
```

Editing and Running Python programs

To open and edit a Python source code file, in a terminal, run the code editor with the name of the file you want to edit (e.g., prog.py):

$ code prog.py

To run a Python program, in a terminal, invoke the Python interpreter (python3) followed by the name of the file with the Python program you want to run (e.g. prog.py):

$ python3 prog.py

Week 1 Code

`welcome.py`

The welcome.py program shows an example Python program. Let’s open it in code and look at some of the main features of a Python program:

$ code welcome.py

Now, lets run the program using the Python interpreter. In a terminal window type:

$ python3 welcome.py

`greeting.py`

Open greeting.py with code and try running it with python. Let’s try to modify the program to prompt the user for a different greeting.

`numbers.py`

numbers.py introduces a second data type: integer. What was the first data type we saw?
Modify numbers.py to cast the user input to a float. Save, run, and test your program.
You can also use the python shell to try small examples. Type python3 in a terminal without a file name to enter the shell. Type Ctrl-D to exit the shell. Note the >>> prompt for the python shell.

Try a few operations in the shell

>>> txt = "hello"
>>> a = 2
>>> x = 3.5
>>> type(txt)
>>> type(a)
>>> type(x)
>>> x + a
>>> a + txt
>>> txt + txt
>>> ans = "2.7"
>>> y = float(ans)
>>> print(y)
>>> type(y)
>>> b = int(y)
>>> type(b)
>>> print(b)
>>> c = int(ans)